The present invention relates to the production of poly(carbonate-co-ester) soft block copolymers by introducing synthetic steps into a process commonly used to synthesize polycarbonates, the melt transesterification method.
Block copolymers possess unique properties which allow for the modification of thermal, mechanical, and other such properties of a polymer that could not be achieved through the synthesis of other types of polymers, such as random copolymers. Poly(carbonate-co-ester) copolymers are known in the art as disclosed in U.S. Pat. No. 4,935,785 and are representative of soft-block copolymers. As compared to polycarbonate homopolymers of the same molecular weight, soft-block copolymers possess improved Theological properties that result in better replication of molded articles.
A variety of block copolycarbonates are known in the art and have been synthesized using the interfacial method, a process which undesirably requires the use of phosgene. Patent Cooperation Treaty (PCT) Pat. Application No. WO 00/26274 discloses the synthesis of block copolycarbonates using a previously-synthesized polyester intermediate with an organic dihydroxy compound and phosgene. Similarly, Japan Patent No. 63199735 discloses the preparation of polycarbonate copolymers by condensation of a prepolymer, which is obtained by a reacting styrene resin and a polycarbonate oligomer with an aromatic dihydroxy compound. The synthesis of these polycarbonate copolymers uses the interfacial method.
In addition, some low molecular weight diacid monomers are not easily incorporated. Several examples of copolyestercarbonate compositions containing adipic acid exist in the literature. See, for example, JP 61149901 (Idemitsu Kosan Co., Ltd., 1986), JP 19660527 (Asahi Chemical Industry Co., 1969), J. Polym. Sci., Polym. Chem. Ed. (1967), 5(4), 927-30. However, these copolymers have been made using adipoyl chloride in the interfacial process; a route which is not very viable commercially. Direct incorporation of diacids using the interfacial process is only possible using longer-chain diacids such as sebacic and dodecanoic acid (DDDA).
The invention discloses the production of a poly(carbonate-co-ester) block copolymer. The method for producing the poly(carbonate-co-ester) block comprises the steps of:
(a) creating a reaction mixture comprising an aromatic dihydroxy compound (e.g., bisphenol A (xe2x80x9cBPAxe2x80x9d), a carbonic acid diester (e.g., diphenyl carbonate (xe2x80x9cDPCxe2x80x9d), and a catalyst,
(b) mixing a polyester prepolymer with the reaction mixture, said polyester prepolymer comprising a diacid, diol or diester, and at least one monomer selected to incorporate the desired properties into the poly(carbonate-co-ester), and optionally pre-reacted with a carbonic acid diester to improve its incorporation and reaction,
(c) bringing the reaction mixture to thermal equilibrium in a melted state, wherein the reaction mixture under thermal equilibrium further comprises a volatile component and a polycarbonate polymer, and
(d) removing the volatile component from the reaction mixture to increase the molecular weight of the polycarbonate.
The method of the invention can be incorporated into conventional melt facilities used in the production of polycarbonates, thereby eliminating the need for phosgene and other solvents.